A linear conveyor that moves a conveyance carriage (slider) along a rail disposed on a base using a linear motor as a driving source has been known (e.g. Japanese Patent Application Laid-open No. 2011-98786). A conveyance path of a linear conveyor may become long depending on the intended use, and in some cases a conveyance carriage may be removed and reinstalled as required. Therefore a movable magnet type linear motor may be used for the linear motor. The movable magnet type linear motor has a linear motor stator which includes a plurality of electromagnets (field magnets) secured to the base in a line and a linear motor mover which is a permanent magnet secured to the conveyance carriage, and provides driving force to the conveyance carriage by controlling the supply of current to the coils constituting the electromagnets. The movable magnet type linear motor has a linear scale constituted by a scale secured to the conveyance carriage and a plurality of sensors disposed on the base, and moves the conveyance carriage to a specific position by controlling the supply of current to the electromagnets based on the detected position by the linear scale.
In the linear conveyor, the form (linear or circular) of the conveyance path and the length of the conveyance path that is required may be different depending on the user, and in some cases, a change may be required later for the form and the length of the conveyance path. In order to easily meet such requirements, the linear conveyor could be unitized. In other words, a unit member is constructed by the base, the rail, the electromagnetics and the sensor of the linear scale. Then the linear conveyor is constructed by linking a plurality of unit members, and a motor controller is disposed for each unit member so that supply of current to the electromagnets of each unit member is individually controlled.
In this case however, the following problems exist. Each conveyance carriage has a unique movement error due to a processing error and an assembly error of a scale, and each sensor of the unit member also has a unique detection error due to an installation error and a characteristic difference. Therefore in order to accurately position the conveyance carriage in the unitized linear conveyors, the movement error of each conveyance carriage of each unit member must be checked in advance, and the movement error in accordance with the conveyance carriage must be corrected for each unit member. In this case, the number of movement error data to be acquired in advance is a number generated by multiplying the number of unit members (motor controllers) by the number of conveyance carriages. However, an operation to acquire this number of movement error data is not easy. Further, in the case of adding a conveyance carriage to an already installed and operating linear conveyor, it is difficult to accurately check the movement error of a conveyance carriage (conveyance carriage that is newly added) for each unit member. Therefore guaranteeing the positioning accuracy for the conveyance carriage that is added later is difficult.